In analyses of biological samples such as clinical tests, an analysis method with a high detection sensitivity and accuracy is desired, because in many cases a trace amount of a compound has to be measured. As such an analysis method, not only a method utilizing a specific interaction, such as an antigen-antibody reaction and an enzyme-substrate reaction, but also a method utilizing a combination thereof with an electric analysis has been attempted to achieve a high detection sensitivity.
For example, patent literature 1 discloses a combination of immunochromatography and a current-detection-type amperometric assay, and patent literature 2 discloses a biosensor in which a protein or an enzyme is immobilized on the gate of a field effect transistor or a single electron transistor. These prior art techniques are characterized by directly detecting a complex formed on the electrode or the gate by a specific interaction.
Further, methods utilizing deposition or adsorption on a sensor caused by a chemical reaction, instead of the utilization of a specific interaction, are disclosed in non-patent literature 1, patent literature 3, and patent literature 4.
Non-patent literature 1 discloses a method in which a silver ion dissolved in a reaction liquid is reduced to deposit silver on a sensor, the silver is reoxidized to generate a silver ion, and the electrochemical change during the reoxidization is detected as a change in current.
Patent literature 3 discloses a method for determining the concentration or amount of a substance to be assayed in a sample, using a labeled antibody in which cholinesterase is bound as a labeling enzyme and measuring the activity of the cholinesterase, wherein the enzyme activity is detected by adsorbing and concentrating an enzyme reaction product, thiocholine, on a noble metal electrode and amplifying the current signal generated by reduction desorption of the thiocholine from the electrode.
Patent literature 4 discloses an apparatus and a method for determining the production amount or the production rate of a thiol compound which is a product of a cyclic reaction of an enzyme-labeled antibody, as the adsorption rate on a gold electrode formed on an insulated gate field effect transistor.
In these prior art techniques, each chemical reaction and each electric detection are carried out under non-flow conditions.
Patent literature 5 discloses a biosensor for detecting a molecule involved in a specific binding of a biomolecule, characterized by comprising (i) a reaction part for carrying out (a) a specific binding reaction and (b) an enzyme reaction, (ii) a detection part for reacting an oxidation-reduction material membrane with the oxidation-reduction reaction product generated by reactions (a) and (b), and (iii) a measurement part for determining the change in dielectric constant by measuring a change in the state of the oxidation-reduction material membrane caused by the reaction thereof with the oxidation-reduction reaction product.
In this prior art technique, no deposit is generated on the sensor, in a similar to those disclosed in patent literatures 1 and 2.    [patent literature 1] Japanese Unexamined Patent Publication (Kokai) No. 2001-153838    [patent literature 2] Japanese Unexamined Patent Publication (Kokai) No. 10-260156    [patent literature 3] Japanese Unexamined Patent Publication (Kokai) No. 2004-257996    [patent literature 4] Japanese Unexamined Patent Publication (Kokai) No. 2007-263914    [patent literature 5] Japanese Unexamined Patent Publication (Kokai) No. 2005-24483    [non-patent literature 1] Analytical chemistry, (U.S.), 2005, vol. 77, p. 579-584